The early detection of viruses including the Human Immunodeficiency Virus (HIV) requires multiplex detection of anti-glycoprotein 41 (gp41) antibodies in biological samples. The availability of high-affinity, highly selective molecular moieties that recognize anti-gp41 antibodies from complex biological mixtures is a critical component for accurate detection of anti-gp41 antibodies that may indicate HIV infections.
Detecting the immune response to an infectious agent can provide a useful in vitro diagnostic surrogate relative to direct pathogen detection. Such assays are commonly used for detecting HIV infection because of HIV's characteristic immunopathology. However, direct detection of HIV viral RNA and p24 antigen is only effective at an early stage of infection, approximately 2-6 weeks of initial exposure. Antibodies against HIV envelope proteins emerge in patients' blood around 3-4 weeks of infection as the viral RNA and p24 levels decline as a result of immunocomplex formation. The high serum level of anti-HIV IgG is maintained throughout the course of clinical latency (2-20+ years), during which time viral antigens are under detection limits until the onset of acquired immunodeficiency syndrome (AIDS). Viral load and CD4+cell counts are mainly used for prognostic purposes to monitor the efficacy of treatments; however viral load is sometimes used for the diagnosis of infant HIV infections where antibody-based assays are not applicable. Assays for anti-HIV antibodies are the most widely used diagnostic test both in cases where infection is presumed to have occurred more than 6 weeks prior to testing, and for epidemiological reasons, to estimate the incidence of HIV in a population, since, with the exception of infant HIV, virtually 100% of the infected individuals express these antibodies. Typically in these assays, immunogenic and conserved antigens from the HIV are expressed as regions of a single chimeric protein. That chimeric protein is then used to capture specific antibodies from the body fluid (e.g. blood, saliva or urine) of potentially infected patients; a positive assay result implies infection. However, the polyclonal diversity of antibodies across a patient population can translate into large variations in assay performance from patient to patient. In addition, the chimeric recombinant proteins are biological reagents, and so may have limitations related to shelf life and batch-to-batch variability. These limitations can adversely influence the performance of a diagnostic test, especially one that is deployed in harsh physical environments. Accordingly, there remains a need for new compositions and assays for the diagnosis of HIV.